Nebulizers, or atomizers as they are sometimes called, are devices that generate a fine spray or aerosol, usually of liquid. A particularly useful application for nebulizers is to provide a fine spray containing a dissolved or a suspended particulate drug for administration to a patient by inhalation.
Piezo-mesh based nebulizers are commonly used to generate aerosols in such drug delivery apparatus, whereby a piezoelectric element vibrates a mesh to produce the fine aerosol spray. In particular, droplets dispensed on the mesh are vibrated by the piezoelectric element to create the spray. There are two principle designs in such piezo-mesh based nebulizers. U.S. Pat. No. 5,938,117 and U.S. Pat. No. 6,983,747 disclose one type of design whereby the piezoelectric element is bonded to a mesh element, whereas U.S. Pat. No. 6,651,650 and U.S. Pat. No. 6,405,934 disclose designs whereby the mesh element is separate from the piezoelectric element. An advantage of having the mesh element separate from the piezoelectric element is that the mesh element is cheaper to manufacture and so can be replaced more frequently.
However, a common disadvantage of all mesh based nebulizers is that a user is required to clean the mesh after use, otherwise the mesh holes may become blocked. There are in the region 5000 2 μm holes in a typical mesh, and these can easily become blocked by particulates in the environment or from salt crystals (i.e. because the drugs are often saline based).
The cleaning method is normally to wash the mesh in warm soapy water for about five minutes, and then rinse and dry the mesh. This process can take as much time as the drug treatment itself, and is therefore a significant burden on the patient. Hence, over time, even with good cleaning the performance of the mesh will deteriorate as more holes become blocked—this may typically happen over a number of weeks. Once the mesh becomes blocked it is very difficult to clean the mesh and remove a particulate which is lodged in a hole, so it is necessary to replace the mesh. Although meshes are designed to last for up to twelve months, they typically have to be replaced every three months, or even on a monthly basis for some patients due to poor cleaning.
Such drug delivery apparatus also typically comprise one or more interchangeable parts, for example interchangeable mouthpieces, interchangeable plunger assemblies and/or interchangeable medication chambers. These interchangeable parts enable a nebulizer to be adapted or customized to best suit the needs of a particular patient. For example, different mouthpieces can be selected depending on the volume of inhalation preferred by a particular user, while different medication chambers can be selected to provide different volumes depending on the drug to be delivered.
A disadvantage of having such interchangeable parts is that the drug delivery apparatus must know which particular part from a set of interchangeable parts is fitted at any particular time, so that the drug delivery apparatus is able to control the delivery of the drug accordingly.
It is an aim of the present invention to provide a drug delivery system that helps alleviate or reduce one or more of the disadvantages mentioned above.